How to Generate PDFs with Async & Multithreading in C#

using IronPdf;
using System.Threading.Tasks;

// Instantiate ChromePdfRenderer
ChromePdfRenderer renderer = new ChromePdfRenderer();

string[] htmlStrings = {"<h1>Html 1</h1>", "<h1>Html 2</h1>", "<h1>Html 3</h1>"};

// Create an array to store the tasks for rendering
var renderingTasks = new Task<PdfDocument>[htmlStrings.Length];

for (int i = 0; i < htmlStrings.Length; i++)
{
    int index = i; // Capturing the loop variable
    renderingTasks[i] = Task.Run(async () =>
    {
        // Render HTML to PDF
        return await renderer.RenderHtmlAsPdfAsync(htmlStrings[index]);
    });
}

// Wait for all rendering tasks to complete
// await Task.WhenAll(renderingTasks);

Imports IronPdf
Imports System.Threading.Tasks

' Instantiate ChromePdfRenderer
Private renderer As New ChromePdfRenderer()

Private htmlStrings() As String = {"<h1>Html 1</h1>", "<h1>Html 2</h1>", "<h1>Html 3</h1>"}

' Create an array to store the tasks for rendering
Private renderingTasks = New Task(Of PdfDocument)(htmlStrings.Length - 1){}

For i As Integer = 0 To htmlStrings.Length - 1
	Dim index As Integer = i ' Capturing the loop variable
	renderingTasks(i) = Task.Run(Async Function()
		' Render HTML to PDF
		Return Await renderer.RenderHtmlAsPdfAsync(htmlStrings(index))
	End Function)
Next i

' Wait for all rendering tasks to complete
' await Task.WhenAll(renderingTasks);

// Batch processing with progress tracking
public async Task<List<PdfDocument>> ProcessBatchAsync(List<string> htmlContents, IProgress<int> progress)
{
    var renderer = new ChromePdfRenderer();
    var results = new List<PdfDocument>();
    var completed = 0;

    var tasks = htmlContents.Select(async html => {
        var pdf = await renderer.RenderHtmlAsPdfAsync(html);
        Interlocked.Increment(ref completed);
        progress?.Report(completed);
        return pdf;
    });

    results.AddRange(await Task.WhenAll(tasks));
    return results;
}

Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks

' Batch processing with progress tracking
Public Async Function ProcessBatchAsync(htmlContents As List(Of String), progress As IProgress(Of Integer)) As Task(Of List(Of PdfDocument))
    Dim renderer As New ChromePdfRenderer()
    Dim results As New List(Of PdfDocument)()
    Dim completed As Integer = 0

    Dim tasks = htmlContents.Select(Async Function(html)
                                        Dim pdf = Await renderer.RenderHtmlAsPdfAsync(html)
                                        Interlocked.Increment(completed)
                                        progress?.Report(completed)
                                        Return pdf
                                    End Function)

    results.AddRange(Await Task.WhenAll(tasks))
    Return results
End Function

public async Task<PdfDocument> RenderWithRetryAsync(string html, int maxRetries = 3)
{
    var renderer = new ChromePdfRenderer();

    for (int i = 0; i < maxRetries; i++)
    {
        try
        {
            return await renderer.RenderHtmlAsPdfAsync(html);
        }
        catch (Exception ex) when (i < maxRetries - 1)
        {
            // Log the exception
            await Task.Delay(TimeSpan.FromSeconds(Math.Pow(2, i))); // Exponential backoff
        }
    }

    throw new InvalidOperationException("Failed to render PDF after maximum retries");
}

Imports System
Imports System.Threading.Tasks

Public Class PdfRenderer
    Public Async Function RenderWithRetryAsync(html As String, Optional maxRetries As Integer = 3) As Task(Of PdfDocument)
        Dim renderer As New ChromePdfRenderer()

        For i As Integer = 0 To maxRetries - 1
            Try
                Return Await renderer.RenderHtmlAsPdfAsync(html)
            Catch ex As Exception When i < maxRetries - 1
                ' Log the exception
                Await Task.Delay(TimeSpan.FromSeconds(Math.Pow(2, i))) ' Exponential backoff
            End Try
        Next

        Throw New InvalidOperationException("Failed to render PDF after maximum retries")
    End Function
End Class

// Thread-safe PDF generation with custom settings per thread
public void ProcessPdfsInParallel(List<string> htmlContents)
{
    Parallel.ForEach(htmlContents, new ParallelOptions { MaxDegreeOfParallelism = Environment.ProcessorCount }, 
        html =>
        {
            // Create a new renderer instance for each thread
            var renderer = new ChromePdfRenderer
            {
                RenderingOptions = new ChromePdfRenderOptions
                {
                    MarginTop = 10,
                    MarginBottom = 10,
                    PaperSize = IronPdf.Rendering.PdfPaperSize.A4
                }
            };

            var pdf = renderer.RenderHtmlAsPdf(html);
            pdf.SaveAs($"output_{Thread.CurrentThread.ManagedThreadId}_{DateTime.Now.Ticks}.pdf");
        });
}

Imports System
Imports System.Collections.Generic
Imports System.Threading
Imports System.Threading.Tasks
Imports IronPdf

' Thread-safe PDF generation with custom settings per thread
Public Sub ProcessPdfsInParallel(htmlContents As List(Of String))
    Parallel.ForEach(htmlContents, New ParallelOptions With {.MaxDegreeOfParallelism = Environment.ProcessorCount},
        Sub(html)
            ' Create a new renderer instance for each thread
            Dim renderer = New ChromePdfRenderer With {
                .RenderingOptions = New ChromePdfRenderOptions With {
                    .MarginTop = 10,
                    .MarginBottom = 10,
                    .PaperSize = IronPdf.Rendering.PdfPaperSize.A4
                }
            }

            Dim pdf = renderer.RenderHtmlAsPdf(html)
            pdf.SaveAs($"output_{Thread.CurrentThread.ManagedThreadId}_{DateTime.Now.Ticks}.pdf")
        End Sub)
End Sub

public async Task<PerformanceMetrics> MeasurePerformanceAsync(string html, int iterations)
{
    var metrics = new PerformanceMetrics();
    var renderer = new ChromePdfRenderer();
    var stopwatch = new Stopwatch();

    // Warm-up run
    await renderer.RenderHtmlAsPdfAsync(html);

    for (int i = 0; i < iterations; i++)
    {
        stopwatch.Restart();
        await renderer.RenderHtmlAsPdfAsync(html);
        stopwatch.Stop();

        metrics.AddMeasurement(stopwatch.ElapsedMilliseconds);
    }

    return metrics;
}

Imports System.Diagnostics
Imports System.Threading.Tasks

Public Class PerformanceMetrics
    ' Assume this class has an AddMeasurement method
    Public Sub AddMeasurement(milliseconds As Long)
        ' Implementation here
    End Sub
End Class

Public Class ChromePdfRenderer
    ' Assume this class has a RenderHtmlAsPdfAsync method
    Public Async Function RenderHtmlAsPdfAsync(html As String) As Task
        ' Implementation here
    End Function
End Class

Public Class PerformanceTester
    Public Async Function MeasurePerformanceAsync(html As String, iterations As Integer) As Task(Of PerformanceMetrics)
        Dim metrics As New PerformanceMetrics()
        Dim renderer As New ChromePdfRenderer()
        Dim stopwatch As New Stopwatch()

        ' Warm-up run
        Await renderer.RenderHtmlAsPdfAsync(html)

        For i As Integer = 0 To iterations - 1
            stopwatch.Restart()
            Await renderer.RenderHtmlAsPdfAsync(html)
            stopwatch.Stop()

            metrics.AddMeasurement(stopwatch.ElapsedMilliseconds)
        Next

        Return metrics
    End Function
End Class